Pressure fluid follow-up servomotor



S- 1949- c. c. WORSTELL 2,477,710

' PRESSURE FLUID FOLLOW-UP SERVOMOTORI Filed Oct. 15. 1945 4Sheets-Sheet 1 INV EN TOR CHARLES C. W LL 1 ATTORNEYS C. C. WORSTELL.

PRESSURE FLUID FOLLOW-UP SERVOMO'IOR 9 4 9 m. Wm

4 Sheets-Sheet 2 Filed 00%. 1.5, 1945 INVENTOR.

A S. C. WORSTELL ATTORNE YS.

L .L E 5 R 0 W C C PRESSURE mum FOLLOW-UP sErwoMoToR Filed Oct. 15, 19454 Sheets- Sheet 4 11V VEN TOR.

AS. 0. WORSTELL ATTORNEYS.

lj "a H6 7 .2 Q 35 6 PatentedAupZ, 1949 PRESSURE FLUID FOLLOW-UP 1sEnvoMoron Charles 0. Worstell, Mollne, m, assignor to Deere & igompany,Moline, 111., a corporation of 1111- Application October 15, 1945,Serial No. 022,242

16 Claims. 1

The present invention relates generally to hydraulic mechanism and isparticularly well adapted for use with tractors and the like for liftingand controlling implements associated therewith.

The principal object of the present invention relates to the provisionof a novel and improved hydraulic control mechanism, which is simpler inconstruction and smootherin operation, but which is strong and durableand inexpensive to manufacture.

A further object relates to the provision of. a hydraulic controlmechanism, in which the movement of the fluid pressure motor issubstantially proportional to the extent of movement of the manualcontrol lever, whereby the position of the manual control lever is anindication of. the position or extent of movement of the fluid pressuremotor. Heretofore, in hydraulic mechanisms of this general class, as thefluid pressure motor approaches the position for which it is adjusted,the valve approaches a closed position, thus throttling the fluid flowthrough the valve and slowing down the movement of the fluid motor.ll'his action is cumulative, with the result that the fluid is caused toleak through the nearly closed valve for a relatively long period oftime during the final seating of the valve. While this is not serious inlow pressure systems, it is the cause of concentrated wear on the valvesurfaces in high pressure circuits, due to the wire drawing effect,producing a considerable degree of localized friction, accompanied bygeneration of heat. More specifically, it is a further object of thepresent invention to provide a hydraulic system of this general class,in which the control valve, which is opened by the manual control leverand closed by the movement of the fluid motor, does not control the mainflow of fluid to the fluid motor. In the accomplishment of this object,a differential valve is provided by which the pressure in the hydrauliccircuit is controlled. Both ends of this differential valve aresubjected to the pressure in the supply duct,

but since the two ends of the valve are unequal in area, the valve isbiased toward a closed position. 'However, the differential valve isopened and closed by the control valve, which merely controls the fluidpressure against the large diameter end of the difierential valve.Hence, the amount of oil flowing through the control valve isnegligible, with the result that not only is the wear on this valvenegligible, but the action thereof is extremely smooth and the fluidmotor can be very accurately controlled.

These and other objects and advantages of my Figure 1 is a schematicdiagram of hydraulicmechanism embodying the principles of my invention;I

Figure 2 is a side elevational view of the hydraulic mechanism:

Figure 3 is a top plan view of the mechanism, a portion of which isbroken away to show the connection of the pump intake duct to thereservoir;

Figure 4 is a sectional elevational view taken along a line t-Ji inFigure 3 and drawn to an enlarged scale;

Figure 5 is a fragmentary elevational view taken in section along a line5- -5 in Figure 2 and drawn to an enlarged scale;

Figure 6 is a fragmentary sectional elevational view taken along a linett in Figure 3 and drawn to an enlarged scale, or along a line 6 -6 inFigure 7;

Figure 7 is a sectional plan view taken along a line 7-7 in Figure 4 anddrawn to an enlarged scale, or along a line i--l in Figure 9;

Figure 8 is a sectional plan view taken along a line in Figures 4 and 9and drawn to the same scale as Figure 7 and Figure 9 is a sectionalelevational view taken along a line t% in Figure 8.

Referring now to the drawings, the hydraulic control mechanism isindicated generally by reference numeral lit, and includes a controlhousing ti having laterally outwardl rojecting lugs 22, provided withvertically extending apertures 23 adapted to receive bolts M forsecuring the housing 2! in operating position on a tractor or the like.A rockshaft housing 25 is disposed at the rear of the control housing 2!and is rigidly connected thereto by bolts 26, which extend throughapertures 27 in a vertically disposed flange it in the control housing2!. The rockshaft housing 25 encloses a transversely disposed rockshaft30, which is journaled in a pair of laterallyextending quills 3i, whichare preferably formed integral with the housing 25, and the rockshaft 3Bextends laterally outwardly of the quills andcarriesa pair of liftingarms 32 on the outer end thereof, which are rigidly fixed thereto in amanner well known to those skilled in the art.

The rockshaft 30 is rocked by means of a rocker arm 40 within thehousing 25, which arm is pivotally connected at 4| to a piston rod 42,the

latter extending forwardly into a cylinder 44, formed integrally withthe control housing 2| and engages a piston 43. The piston 43 andcylinder 44 comprise a fluid pressure actuated motor in the form of aram, which controls the rocking of ther ockshaft 30. The forward end ofthe cylinder 44 is closed by a cylinder head 45, which is preferablycast integrally with the housing 2|.

Fluid is supplied under pressure to the forward end of the cylinder 44,thereby forcing the piston 43 rearwardly and rocking the rockshaf-t 39in a clockwise direction, as viewed in Figure 4.

The fluid is supplied under pressure by. means of awconventionalconstant displacement type gear pump 59 connected with the controlhousing 2| through a high pressure supply duct 52 and a low pressurereturn duct 53. The return duct 53 is connected to an opening 54 nearthe bottom of the rockshaft housing 55 by means of an elbow fitting 56(Figure 3). Thus, the rockshaft housing 25 also serves as a reservoirfor the hydraulic fluid, such as oil.

The high pressure supply duct 52 is connected by means of a suitablefitting 51 with a supply duct passage 58 within the housing 2| above thecylinder 44, the duct 58 extending laterally inwardly from one side ofthe housing 2| and intersecting a rearwardly extending pass-age 59. Anexhaust port 60 in the rear end of the passage 59 provides a seat for apoppet type valve 6| (Figure 8), which is part of a differential valve62, which i also includes a piston 63, formed integrally with the poppetvalve 6|. The piston '63 is of larger diameter than the valve 6| and isslidably disposed in a cylindrical passage 64, which extends rearwardlyint-o communication with the reservoir 65 in the housing 25, but isclosed by means of a threaded plug 66. Normally, the differential valve62 is urged by means of a spring 61 behind the piston 63 toward a closedposition in the seat of the exhaust port 60, but can be forced away fromthe seat 60 by pressure within the passage 59, to permit fluid thereinto be discharged through an opening 68, which communicates with areservoir 69 within the control housing 2|. The rear end of thereservoir 69 communicates with th reservoir '65 in the rockshaft housing25. A relief hole I prevents any pressure from building up between thepiston 63 and the forward end of the enlarged passage 64, the hole alsocommunicating with the reservoir 69.

Immediately in front of the seat 60 is a vertically extending passage15, which connects the passage 59 with a check valve passage 16, withinwhich is disposed a check valve 11 of the poppet type having a head 18disposed within a chamber 19 at one end of the passage 16. The head 18of the check valve I1 is seated in the end of the passage 16 and isurged toward seated relation by a compression spring 89, which bearsagainst a plug 8| in the outer end of the chamber 19. A plug 82 closesthe other end of the passage (Figures 3 and 9).

A forwardly extending duct 85 intersects the chamber 19 at its rear endand intersects a downwardly extending passage 86 at its forward end. Thepassage 86 communicates with the forward end of the cylinder 44 of thefluid pressure motor.

The stem of the check valve 11 bears against a camming surface 90 of a.valve plunger 9|, which is slidably disposed in a fore and aft extendingcylindrical passage 92, which communicates at its forward end with thereservoir 69 and the valve plunger 9| is shifted forwardly in thecylindrical passage 92, but the camming surface has a forwardlyextending flat portion 93 which permits the valve 11 to remain closedunder the action of its compression spring 80 when the valve plunger 9|is shifted rearwardly within the passage 92. The forward end of thevalve plunger 9| has a piston 98, which flts closely within the forwardend of the passage 92, thereby preventing any flow of fluid f-orwardlyinto the reservoir 69, and is also provided with a spool or pistonportion 94 at the rear end of the valve plunger 9|, which prevents anyflow of fluid from the passage 16 rearwardly into the reservoir 65.Between the two spool or piston portions 98, 94, the valve member is ofsmaller diameter to permit a flow of oil therealong.

The valve cylinder 92 is provided with a valve port 95, whichcommunicates through a downwardly and inwardly inclined passage 96 withthe cylinder 64 in which the differential valve piston 63 is slidablydisposed. The valve port is controlled by the piston portion 94 of thevalve member 9|, which can be shifted axially within the cylinder 92between a normal or inactive position, as shown in Figure '7, in whichthe valve port 95 is open slightly to the rear of the piston 94, therebyrelieving the pressure within the differential valve cylinder 64, and anactive position in which the piston 94 closes the port 95 againstdischarge of fluid rearwardly into the reservoir 65 and connects theport 95 in communication with the check valve passage it to permit fluidto'flow from the latter along grooves 91 in the stem of the check valve11 into the cylindrical passage 92 and from there into the cylinder 64through the valve port 95.

The operation of the mechanism thus far described is as follows:

' With the valve member 9| in its inactive position shown in thedrawings, the fluid supplied by the pump through the conduit 52 flowsthrough ducts 58, 59, through the exhaust port 60 past the poppet valve6|, and into the reservoir 69 through the discharge aperture 68. Only aslight pressure is required to force open the differential valve 62, forthe spring 61 is a weak spring. The fluid in the passage 59 is also freeto flow upwardly (Figure 7; downwardly in Figure 2) through the verticalpassage 15 into the check valve passage 16, and into the valve cylinder92. The valve port 95, however, is closed against flow of fluid from thecylinder 92, and since the check valve 11 is seated by the spring 80which is stronger than the differential valve spring 61, no fluid flowsthrough the check valve 11 into the main cylinder 44. Hence, all of thefluid from the supply duct 52 is returned to the reservoir 69 throughthe discharge opening 68.

The load on the lifting arms 32 can be raised by shifting the valvemember 9| rearwardly until the piston 94 uncovers the valve port 95 topermit fluid to flow through the latter into the differential valvecylinder 64, thereby substantially equalizing the pressure in thedifferential valve cylinder 64 and in the passage 59, but, as shown inFigure 8, the cross sectional area of the differential valve piston 69is appreciably greater than the area of the head of the poppet valve 6|,and therefore the force of the oil pressure against the piston 69overcomes the force which reacts against the head of the valve with theresult that the differential valve 02 is shifted to the right, as viewedin Figure 8, until the poppet valve BI seats in the exhaust port 60.

The fluid pressure within the supply passages 58, 59 now increases, andforces the check valve to from its seat in the end of the passage 16against the pressure of the spring 80, thereby permitting the oil toflow through the vertical passage 15, past th check valve 18 and throughthe cylinder supply ducts 85, 00 into the forward end of the cylinder 44of the fluid pressure motor.

a The fluid pressure in the cylinder 44 causes the valve head BI,exhausting the fluid from the sup-- ply passages 58, 59 through theopening 68. This permits the check valve 19 to close against its seat bythe action of th spring 80 and by the pressure of the fluid in thecylinder 44 due to the weight of the load on the rockshaft, which isthus locked in adjusted position.

Inasmuch as only a very small quantityof oil passes through the port 95,either when starting or stopping the fluid motor, the wear on the port95 and spool or piston 94 is negligible. Furthermore, the action of thedifferential valve 62 in opening and closing the exhaust port 60 is fastand positive, for as soon as the pressure in the cylinder 64 actingagainst the piston 03 overbalances the pressure against the valve head6| it closes the latter with a quick positive action. Similarly, whenthe pressure isrelieved from the cylinder 64, the pressure against thehead BI suddenly and positively opens the valve GI, so that there is noprotracted time in which the valve BI is cracked open under pressure andtherefore there is very little friction against the valve seat or valveand very little heat developed.

The valve member Si is controlled by a manually operated lever iflll,which is fixed to a pivot shaft IOI journaled in a pair of bosses i022within the reservoir portion $9 of the housing ii. A crank arm M13 isfixed to the pivot shaft till between the bosses m2 and has a bifurcatedend that is pivotally connected by a pin its to a link Hi5 which extendsforwardly therefrom. The link I05 is pivotally connected by a pin Illsto a beam Mil intermediate the ends thereof, which is disposed generallyvertically in the forward end of the reservoir 69. The upper end of thebeam Hill is swingably connected by'a pin its to the forward end of thevalve member M, the latter being bifurcated to receive the upper end ofthe beam lift. The lower end of the beam lfl'i is pivotally connected bya pin its to a longitudinally extending connecting link Ht, whichextends rearwardly through the reservoir 69 into the rockshaft housing25, where it is connected by a pivot bolt ii i to the rocker arm atbetween the rockshaft 3t and the piston rod connection d II. The beamitl constitutes a difierential con nection between the manuallycontrolled lever W0, the valve member 9i, and the arm at on therockshaft 3t, which provides a follow-up action in which the manuallycontrolled lever I00 can be moved by the operator to any desiredposition, whereupon the piston 43 will move within the cylinder 44 to aposition corresponding to 5 the setting of the lever I00, upon which thevalve member 9| will be shifted to its inactive position to stop thepiston 43 the desired point in its range of movement.

For example, the load can be raised apredetermined extent by moving thelever I00 rearwardly an amount proportional to the extent of desiredmovement of the load, thereby pulling the link I05 rearwardly andswinging the beam I01 in a counter clockwise direction about the axis ofthe lower pivot I09, as viewed in Figure 4. The position of the pivotI09 is momentarily fixed because the rockshaft 30 is locked in itspresent position of adjustment, and hence the swinging of the beam I01shifts the valve member 9I rearwardly within the'valve cylinder 92,admitting fluid pressure through the port 95 to the differential valvecylinder 64 and effecting a rearward movementofthe piston 43 in themanner described above. As the piston 43 and rocker arm 40 moverearwardly, the beam I01 is swung angularly in a clockwise'directionabout the pivot pin I06 as a fulcrum to shift the valve member inforwardly, returning the latter to the neutral or inactive position, forthere is suilicient friction in the mounting of'the control lever I00 toprevent it being shifted by movement of the piston. Hence, when thepiston 43 reaches the desired position as predetermined by the positionof the lever I00, the valve piston 94 uncovers the valve port 95 andrelieves the pressure in the valve cylinder 64 thereby causing themovement of the piston 43 to be arrested.

Conversely, the load can be lowered by moving the lever I00 forwardly toany desired position within its range, thereby swinging the beam I 01 ina clockwise direction about the pivot I09 and shifting the valve member9i forwardly from its neutral position, thereby moving the cammingsurface 90 against the stem of the check valve 11, forcing the latteraway from its seat in the end of the passage 16 and releasing fluid fromthe cylinder 44 through the passages 86, 85 and 19. In this direction ofmovement of the valve member ill, the valve piston 94 merely uncoversthe valve port 95 to a greater extent, which does not affect thedifferential valve 62 but permits the flow of oil from the supplypassages 58, 59 to exhaust through the opening 68 to the reservoir. Thefluid from the cylinder d4 flows downwardly through the vertical passage15 and also flows through the exhaust port and is discharged through theopening 68, allowing the piston is to move forwardly in th cylinder 44and acting through the link III] to shift the 50 beam It? in a counterclockwise direction about the pivot I06, thereby restoring the valvemember ill to its neutral position and letting the check valve 18 dropinto its seat, with the result that when the piston d3 reaches theposition 5 predetermined by the setting of the control lever illll, thecheck valve 18 closes and locks the piston and rocker arm 00 againstfurther movement.

A- guide plate II5 for the control lever tilt is secured to the side ofthe housing M by means 70 of a pair of bolts IIB, which extend intothreaded apertures i IT in the side of the housing 2|. The guide plateH5 is provided with an arcuate slot M8, which receives a bolt H9 securedwithin the slot II8 by a thumb nut I20. By loosening the thumb nut I20,the bolt can be adjusted to any not necessary since the implement isusually lifted to the full extent of movement of the rockshaft.

In case the load .on the rockshaft is excessive, or in case theimplement encounters an obstruction during the raising operation, thepressure in the supply ducts 58, 59 is limited by means of an excesspressure relief valve I25 of the poppet type, disposed within a passageI26 in the housing 2| intersecting the supply duct 58. A strongcompression spring I21 holds the valve I25 in its seat during normaloperation, the spring I21 bearing against a plug I28, threaded in therear end of the passage I26 and the plug I28 is provided with an axiallyextending aperture I29, through which the fluid is returned to thereservoir 55 when the pressure in the passage 58 becomes great enough tolift the check valve I 25 against the action of the spring I21.

In order to place the control lever I00 in a position convenient to theoperator, the operator's seat I 35 is supported on a forwardly extendingstandard I36, which is rigidly fixed, as by welding, to a transverselyextending angle member I31, which lies along the upper edge of theflange 28 on the housing 2| and has a downwardly turned flange which isapertured to receive the bolts 26. Thus, when the operator sits in theseat I35, the control lever I00 is disposed conveniently between hisknees.

The areas of the inner surfaces of the piston portions 94, 98- of thevalve member 9i which are subjected to fluid pressure within the valvepas sage 92 are made intentionally unequal to bias the member 9| in onedirection and thus to take up any looseness in the pivot joints betweenthe valve member 9i, the beam I01, link I05, arm I03, rod IIO, androcker arm 40. Specifically, the area of the piston portion 98 exposedto pressure within the passage 92, indicated at d, is slightly greaterthan that indicated at d of the portion 94, thereby tending to urge thevalve member 9I forwardly against the pivot pin I00. The forward andrear portions of the passage 92 have corresponding portions d, d ofunequal diameter to accommodate the respective valve portions 98, 94.This eliminates lost motion in all of the joints and provides greateraccuracy in control.

I do not intend my invention to be limited to the exact details shownand described herein, except as set forth in the claims which follow.

I claim:

1. Hydraulic mechanism comprising a fluid pressure motor and a controlhousing associated therewith having a fluid supply duct connected withsaid motor and an exhaust port communicating with said duct, a checkvalve in said duct between said port and said motor adapted to normallyprevent fluid from flowing through said duct from said motor, adifferential valve in said housing controlling said port, and a controlvalve member for controlling said differential valve, said valve memberbeing shiftable into engagement with said check valve to open thelatter.

2. Hydraulic mechanism comprising a fluid pressure motor, a fluid supplyduct connected with said motor, said duct having an exhaust port, acheck valve'in said duct between said port and said motor adapted tonormally block the duct against flow of fluid away from said motor, adifierential valve comprising a poppet type valve head for closing saidport and a piston for controlling said valve head, means defining apassage communicating with said supply duct for subjecting said pistonto the pressure in said duct in opposition to the pressure against saidvalve head, said piston having a greater area than said head for biasingthe latter toward closed position in said port when subjected to equalpressure, and a control valve in said passage means for relieving thepressure against said piston to permit said valve head to be forced awayfrom said port by the fluid pressure in said duct, whereby the fluid isby-passed through said exhaust port and said check valve closes to prevent return flow from said motor, and a common control element for saidcontrol valve and said check valve, said element being shiftable to openboth said control valve and said check valve to permit flow of fluidfrom said motor to said port.

3. Hydraulic mechanism comprising a fluid pressure ram and a controlhousing associated therewith having a fluid supply duct connected withsaid ram and an exhaust port communicating with said duct, a check valvein said duct between said port and said ram adapted to normally blockthe duct against flow of fluid away from said ram, a differential valvecomprising a valve head seatable in said exhaust port and shiftableaxially away from said port by fluid pressure within said duct and apiston for controlling said valve head, a cylinder in which said pistonis slidably disposed, passage means in said housing connecting saidsupply duct with said cylinder for applying fluid pressure to saidpiston in a direction tending to close said port against pressure insaid duct, said piston having a greater area than said head for closingthe latter when subjected to equal fluid pressure, and a control valvein said passage means for relieving the pressure against said piston topermit said valve head to be forced away from said port by the fluidpressure in said duct, whereby the fluid is bypassed through saidexhaust port and said check valve closes to prevent return flow fromsaid ram, and a common control element for said control valve and saidcheck valve, said element being shiftable to open both said controlvalve and said check valve to permit flow of fluid from said ram to saidport.

4. Hydraulic mechanism comprising a fluid pressure ram and a controlhousing associated therewith having a fluid supply duct connected withsaid ram and an exhaust port communicating with said duct, a check valvein said duct between said port and said ram adapted to normally blockthe duct against flow of fluid away from said ram, a differential valvecomprising a valve head seatable in said exhaust port and shiftableaxially away from said port by fluid pressure within said duct and apiston attached to said head for controlling the latter, a cylinder inwhich said piston is slidably disposed, passage means in said housingconnecting said supply duct with said cylinder for applying fluidpressure to said piston in a direction tending to close said portagainst pressure in said duct, said piston having a greater area thansaid head for closing the latter when subjected to equal fluid pressure,

76 a compression spring disposed within said cylinder engaging saidpiston for urging said diflerential valve toward closed position, and acontrol valve in said passage means for relieving the pressure againstsaid piston to permit said valve head to be forced away from said portby the fluid pressure in said duct, whereby the fluid is by-passedthrough said exhaust port and said check valve closes to prevent returnflow from said ram, and a common control element for said control valveand said check valve, said element being shiftable to open both saidcontrol valve and said check valve to permit flow of fluid from said ramto said port. I

5. Hydraulic mechanism comprising a. fluid pressure motor and a controlhousing associated therewith having a fluid supply duct connected withsaid motor and an exhaust port communicating with said duct, a checkvalve in said ductpiston is slldably disposed, an inlet port insaidcylinder through which fluid can be conducted for applying pressure tosaid piston in a direction tending to shift said valve head into closingrelation with said exhaust port, said housing having a cylindricalpassage communicating with said supply duct and having a valve portconnected with said cylinder inlet port, a spool valve member slidableover said valve port to control fluid flow into said valve cylinder,said, piston having a greater area than said valve head for biasing thelatter toward closed position in said exhaust port when subjected to thepressure in said supply duct, and a common control element for saidspool valve member and said check valve, shiftable in one direction toshift said spool valve member to open said valve port to pressure withinsaid passage to actuate said diflerential valve to close said exhaustport and direct the fluid to said motor, said control element beingshiftable in the opposite direction to slide said spool valvemember-over said valve port to block oil fluid pressure thereto, saidcontrol element being shiitable further into engagement with said checkvalve to open the latter and exhaust fluid from said motor.

6. Hydraulic mechanism comprising a fluid pressure motor and a controlhousing associated therewith having a fluid supply duct connected withsaid motor and an exhaust port communieating with said duct, a checkvalve in said duct between said port and said motor adapted to normallyblock the duct against flow of fluid away from said motor, adifferential valve comprising a valve head seatable in said exhaust portand shiftable axially away from said port by fluid pressure within saidduct and a piston for controlling said valve head, a cylinder in whichsaid piston is slidably disposed, an inlet port in said cylinder throughwhich fluid can be conducted for applying pressure to said piston in adirection tending to shift said valve head into closing relation withsaid exhaust port, said housing having a cylindrical passagecommunicating at one end with said supply duct and having a. dischargeport at the other end thereof and an intermediate valve port connectedwith said cylinder inlet port, a valve plunger slidable in saidcylindrical passage and having a spool valve member slidable over saidvalve port to Selectively connect the latter. with said supply duct orwith said discharge port, said piston having a greater area than saidvalve head for biasing the latter toward closed position in said exhaustport when subjected to the pressure in said supply duct and means onsaid valve plunger engageable with said check valve to open the latterwhen said valve plunger is shifted to a position in which said valveport is connected with said discharge port.

7. Hydraulic mechanism comprising a fluid pressure motor and a controlhousing associated therewith having a fluid supply duct, an exhaust portin said duct and a passage connecting said supply duct with said motor,a diflerential valve comprising a valve head seatable in said exhaustport and shiftable axially away from said port by fluid pressure withinsaid duct and a piston for controlling said valve head, a cylinder inwhich said piston is slidably disposed, an inlet port in said cylinderthrough which fluid can be conducted for applying pressure to saidpiston in a direction tending to shift said valve head into closingrelation with said exhaust port, said housing having a cylindricalpassage communicating at one end with said supply ductand having adischarge port at theother end thereof and an said discharge port, saidpiston having a greater area than said valve head for biasing the lattertoward closed position in said exhaust port when subjected to thepressure in said supply duct, and a check valve disposed in said motorconnected passage for locking fluid in said motor, said-valve memberhaving a camming surface engageable with said check valve when saidvalve member is shifted to connect said valve port with said dis chargeport.

8. The combination set forth in claim 7, including the further provisionof a manual control lever and mechanical means differentially connectingsaid lever, said fluid pressure motor, and said valve member, soconstructed and arranged that said valve member can be actuated by saidlever to connect said valve port with said supply duct, thereby closingsaid differential valve to block said exhaust port, diverting fluid tosaid motor to drive the latter, said motor acting through saiddifferential connecting means to shift said valve member to connect saidvalve port with said discharge port, thereby opening said difierentialvalve to stop said motor.

9. Hydraulic mechanism comprising a fluid pressure ram and a controlhousing associated therewith having a fluid supply duct connected withsaid ram and an exhaust port communicating with said duct, a check valvein said duct between said port and saidram adapted to normally preventfluid from flowing through said duct from said ram, a differential valvein said housin controlling said port, a control valve member for.

controlling said difierential valve, said valve member being shiftableinto engagement with in one direction to open both said control valve.

. 11 to stop said ram at a position determined by the position of saidlever. v

10. Hydraulic mechanism as set Iorth in claim 9, including the furtherprovision of means for imposing fluid under equal pressure on saidcontrol valve member continuously in relatively opposite directions,said member having surfaces of slightly unequal area, against which saidpressure is imposed, thereby biasing said valve member lightly in onedirection to take up any looseness in connections of said link means.

11. Hydraulic mechanism comprising a fluid pressure ram, a fluid supplyduct connected with said ram, said duct having an exhaust port, a checkvalve in said duct between said port and said ram adapted to normallyblock the duct against flow of fluid away from said ram, a dif- 12 asaid passage to actuate said differential valve to close said exhaustport and direct the fluid to said motor, said control element beingshiitable in the opposite direction to slide said spool valve ated bysaid control lever to effect a movement of said motor, the latter actingthrough said beam I to actuate said element to stop said motor at aferential valve comprising a valve head for clos- .ing said port and apiston ,for controlling said valve head, means defining a passagecommunicating with said supply duct for subjecting said piston to thepressure in said duct in opposition to the pressure against said valvehead, said piston having a greater area than said valve head for biasingthe latter toward closed position in said port when subjected to equalpressure, a control valve in said passage means for relieving thepressure against said piston to permit said valve head to be forced awayfrom said port by the fluid pressure in said duct, whereby the fluid isbypassed through said exhaust port and said check valve closes toprevent return flow from said ram, a common control element for saidcontrol valve and said check valve, said element being shiitable andsaid check valve to permit flow of fluid from said ram to said exhaustport, a manual control lever, a control beam, and link means connectingsaid element, said control lever and said ram with said control beam, soconstructed and arranged that said common control element can beactuated by said control lever to effect a movement of said ram, thelatter acting through said beam to actuate said element to stop said ramat a position determined by the position of said lever.

12. Hydraulic mechanism comprising a fluid pressure motor and a controlhousing associated therewith having a fluid supply duct connected withsaid motor and an exhaust port communicating with said duct, a checkvalve in said duct between said port and said motor adapted to normallyblock the duct against flow of fluid away from said motor, a,differential valve comprising a valve head seatable in said exhaust portand shiftable axially away from said port by fluid pressure within saidduct and a piston for controlling" said valve head, a cylinder in whichsaid piston is slidably disposed, an inlet portin said cylinder throughwhich fluid can be conducts; for applying pressure to said piston in adirection tending to shift said valve head into closing relation withsaid exhaust port, said housing having a cylindrical passagecommunicating with said supply duct and having a valve port connectedwith said cylinder inlet port, a spool valve member slidable over saidvalve port to control fluid flow into said valve cylinder, said pistonhaving a greater area than said valve head for biasing the latter towardclosed position in said exhaust port when subjected to the pressure insaid supply duct, and a common control element for said spool valvemember and said check valve, shiftable in one direction to shift saidspool valve member to open said valve port to pressure within positiondetermined by the position-of said lever.

13. Hydraulic mechanism comprising a fluid presssuremotor and a controlhousing associated therewith having a fluid supply duct connected withsaid motor and an exhaust port communicating with said duct, a checkvalve in said duct between said port and said motor adapted to normallyblock the duct against flow of fluid away from said motor, adifierential valve comprising a valve head seatable in said exhaust portand shiftable axially away from said port by fluid pressure within saidduct and a piston for controlling said valve head, a cylinder in whichsaid piston is slidably disposed, an inlet port in said cylinder throughwhich fluid can be conducted for applying pressure to said piston in adirection tending to shift said valve head into closing relation withsaid exhaust port, said housing having a cylindrical passagecommunicating at one end with said supply duct and having a dischargeport at the other end thereof and an intermediate valve port connectedwith said cylinder inlet port, a valve plunger slidable in saidcylindrical passage and having a spool valve member slidable over saidvalve portto selectively connect the latter with said supply duct orwith said discharge port, said piston having a greater area than saidvalve head for biasing the latter toward closed position in said exhaustport when subjected to the pressure in said supply duct, means on aidvalve plunger engageable with said check vali x to open the latter whensaid valve plunger is shifted to a position in which said valve port isconnected with said discharge port, a manual control lever, I

a control beam, and link means connecting said plunger, said lever, andsaid motor with said control beam, so constructed and arranged that saidplunger can be actuated by said control lever to effect a movement ofsaid motor in either direction, said motor acting through said beam toactuate said plunger to stop said motor at a position determined by theposition of said lever.

14. Hydraulic mechanism as set forth in claim 13, including the furtherprovision that said plunger is provided with a piston portion spacedfrom said spool member and having a reduced diameter portiontherebetween extending across the opening to said supply duct, saidspool member and said piston portion having slightly unequal opposedareas subjected to the pressure in said supply duct to lightly bias saidplunger in one direction to take up any looseness in connections of saidlink means.

15. In fluid-pressure apparatus having a source of fluid-pressure supplyand a fluid-pressure-receiving device: control means comprising meansproviding a fluid-pressure-transmitting duct having an inlet port forconnection to the source of fluid-pressure and an outlet port forconnection to the fluid-pressure-receiving device; means providing anexhaust port communicating with said duct intermediate the inlet andoutlet ports thereof to enable a portion of the duct to accommodatereturn of fluid pressure from the fluidpressure-receiving device; meansincluding a check valve normally efiective to close the duct between theexhaust and outlet ports against the return of fluid pressure from thefluid-pressurereceiving device; difierential valve means cooperativewith the exhaust port to control opening and closing thereof; and apositionable control member for controlling the differential valve meansand cooperative with the check valve to open said check valve.

16. In fluid-pressure apparatus having a source of fluid-pressure supplyand a fluid-pressure-receiving device: control means comprising meansproviding a fluid-pressure-transmitting duct having an inlet port forconnection to the source of fluid-pressure supply and an outlet port forconnection to the fluid-pressure-receiving device; means providing anexhaust port communicating with said duct intermediate the inlet andoutlet ports thereof to enable a portion of the duct to accommodatereturn of fluid pressure from the Siuid-pressure-receiving device; meansincluding a check valve normally effective to close the duct between theexhaust and outlet ports against the return of fluid pressure from thefluid-pressure-receiving device; means for opening and closing theexhaust port, including a positionable difierential valve having a pairof fluidpressure-receiving areas, one of which is greater than theother, and passage means connected between said difierential valve andthe duct for subjecting said areas to equal fluid pressure from saidduct, said differential valve being thereby biased toexhaust-port-closing position; a control valve cooperative with saidpassage means for relieving fluid pressure on the greater area portionof the differential valve so that fluid pressure on the smaller areacauses the differential valve to effect opening of the exhaust port andfluid pressure carried by the duct from the inlet port is by-passedthrough the exhaust port while the aforesaid check valve means isclosed; and a common control element cooperative with both the controlvalve and the check valve means and positionable to effect opening ofthe check valve means and pressure-relieving action of the control valveon the differential valve to effect return of fluid pressure through theduct from the ,fluid-pressure-receiving device to the opened exhaustport.

1 CHARLES C. WORSTELL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 354,020 Morey Dec. 7, 1886410,184 Ongley Sept, 3, 1889 2,069,540 Sanford Feb. 2, 1937 2,330,739Piron Sept. 28, 1943 FOREIGN PATENTS Number Country Date 412,756 GreatBritain July 5, 1934 586,773 France Jan. 9, 1925 53,192 Austria Apr. 25,1912

